Ironwood, American Hornbeam or Blue Beech,
Carpinus caroliniana
Betulaceae or Birch Family
 

Small tree with dark gray, smooth bark.  Trunk has smooth ridges that make it look like rippling muscles. Leaves egg-shaped, double-toothed, not opposite each other on the twig.  Male flowers catkins in mid spring.  Female flowers green, resembling a string of funny hats (see end of twig below center).  Fruits are tiny nuts, attached to leaf-like bracts with 3 points, in a dangling cluster. Bracts turn brown as the fruits mature (below).

Native tree of bottomlands and floodplains.  Occasional in the floodplain of Connelly's Run.  A splendid specimen occurs next to the north bridge on the Riverway bike path.

Hornbeam (Ostrya Virginiana) is also called ironwood.  It has very similar leaves and flowers.  The bark, however, is brownish, grooved and shreddy, and the fruits are small nuts enclosed in unlobed bladders in a cluster like a tiny pinecone.